The present invention relates to the fields of forming coatings on substrates and assembling devices having coated elements.
The deposition of materials to form coatings on curved substrates is well known and finds utility, for example, in the manufacture of lamps. In the manufacture of lamps, particularly lamps which include a hermetically sealed light emitting chamber (i.e., a lamp burner) such as halogen lamps or high intensity discharge (“HID”) lamps, it is often desirable to deposit one or more materials to form a coating on at least a portion of the surface of the lamp burner. For example, it is well known to deposit materials such as infrared reflecting (“IRR”) material, ultraviolet reflecting material, heat reflecting material, and visible spectrum radiation reflecting material to form coatings on the surface of lamp burners.
A known method of manufacturing lamps having a coating formed on at least a portion of the surface of the lamp burner includes the sequential steps of (i) providing a lamp burner envelope formed from a generally tubular section of light transmitting material; (ii) positioning one or more electrical leads so that each lead provides an electrical connection from the interior of the light emitting chamber to the exterior of the chamber; (iii) sealing the lamp burner envelope to hermetically seal the burner envelope to the leads to thereby seal the light emitting chamber; and then (iv) depositing one or more materials to form a coating on at least a portion of the surface of the lamp burner.
There are many disadvantages in this method of manufacturing such lamps due to the sequence of the steps of (a) sealing the lamp burner and (b) forming the coating on the sealed lamp burner. Some of the disadvantages result from the difficulty of uniformly depositing the material or materials on the elongated shape and generally circular cross-section of the lamp burners, a process which requires the rotation of each individual lamp burner about its longitudinal axis from the outside once the leads are installed and the ends of the burner are sealed. Other disadvantages include the limited throughput in the deposition process as a result of the amount of area occupied by the carrier required to hold and rotate each lamp burner. Still other disadvantages result from the limitation on the temperature of the reactive process caused by the presence of the elements of the burner other than the envelope. Further disadvantages result from the inability to test the quality of the coating before the coated substrate is used in additional manufacturing steps, e.g., the time and expense of completing the burner before discovering a defective coating results in the loss of the entire burner rather than the relatively inexpensive, defectively coated burner envelope. Still other disadvantages result from the inability to use the coating to facilitate other manufacturing steps such as the positioning of the leads within the envelope in the aligning and sealing process.
With respect to the difficulty in obtaining uniform deposition, the processes used to form coatings on substrates such as lamp burners include chemical vapor deposition (“CVD”) and sputter deposition. One prior art method and apparatus for forming a coating on substrates by sputter deposition is disclosed in U.S. Pat. No. 5,849,162 to Bartolomei et al., the content of which is incorporated herein by reference. In the Bartolomei et al. process, one or more substrates are supported by a carrier and carried past one or more sources of the material or materials to be deposited, e.g., sputtering targets in a sputter deposition process, by a rotating drum or a linearly transported planar surface.
It is desirable that the materials deposited on the surface of the lamp burner form a coating which possesses uniform physical characteristics throughout the coated surface about the circumference of the lamp burner. In this way the physical characteristics of the coating on any one portion of the surface of the lamp burner are the same as the physical characteristics of the coating on the other portions of the surface of the lamp burner.
A known process for uniformly coating elongated objects having a generally circular cross-section, here described in connection with the coating of lamp burners, includes the steps of (a) supporting an array of the lamp burners on a carrier (such as a cylindrical drum or planar surface as disclosed in Bartolomei et al.); (b) rotating each lamp burner in the array about its longitudinal axis; and (c) carrying the rotating array past one or more sources of the material or materials to be deposited. By rotating each lamp burner about its longitudinal axis while depositing the material or materials on the selected portions of the surface of the lamp burner to form the coating, each portion of the circumference of the lamp burner the material or materials deposited may be uniformly deposited about the circumference of each lamp burner thus providing uniformity in the physical characteristics of the coating about the entire coated surface of the lamp burner.
The mounting of each end of each lamp burner in the array to a mechanical means for rotating the burner requires redundant, complex and expensive tooling in the coating apparatus. In one aspect, it is an object of the present invention to provide a novel coating method and apparatus for forming a uniform coating on an array of lamp burner envelopes which requires less complex and thus less expensive tooling for the rotation of each lamp burner or other substrate about its longitudinal axis during the coating process. This and other objects may be achieved by the novel apparatus and method for rotating a plurality of lamp burner envelopes about the longitudinal axis thereof while moving the envelopes past one or more sputtering sources.
With regard to the throughput of the deposition process, it is desirable to maximize the throughput by maximizing the number of substrates which may be mounted on the carrier. It is common in known processes for each individual substrate rotation means to require more space on the carrier than the individual substrate. Because each substrate is mounted on an individual axial rotation means, the maximum density of the array of lamp burners which may be carried per surface area of the carrier is severely limited. In another aspect, it is an object of the present invention to provide a novel method and apparatus for forming a coating on an array of substrates with significantly improved throughput.
With respect to temperature limitations, it is often desirable to coat substrates using a reactive coating method such as disclosed in the aforementioned Bartolomei et al. patent. In that process, a material such as silicon is deposited and reacted with a gas such as oxygen so that the coating on the surface of the substrate comprises silicon dioxide, a reaction which generally occurs more readily at higher temperatures. While the temperature at which the reactive coating is deposited on the substrate in a reactive sputter deposition process is generally within the range of 25° C. to 125° C. and is limited to about 200° C. or below, the time required to form a completely reacted coating on a substrate may be reduced by depositing the coating material or materials at a rate in excess of the rate at which all of the deposited materials will be reacted with the reactive gas in the reactive coating apparatus, and thereafter removing the substrates from the reactive coating apparatus for baking in a reactive atmosphere at temperatures greater than the temperature of the deposition process. The elevation of temperature in the baking process reduces the total time required to obtain a fully reacted coating on a substrate and thus improves the efficacy of the coating process. Generally, the amount of time required to complete the reaction is inversely related to the baking temperature, and the uniformity of the coating is generally enhanced by higher baking temperatures.
However, the temperature of the baking process may be significantly limited by the non-substrate components being baked. Where, for example, electrical leads and other components of a completed lamp burner are present, such electrical leads will be damaged if exposed to high temperatures in a reactive atmosphere such as air which contains a significant amount of oxygen. For example, the baking temperature of a lamp burner having tungsten and molybdenum electrical leads must be limited to less than about 400° C. in an atmosphere comprising essentially of normal dry air to prevent damage to the electrical leads due to oxidation of the leads. Thus, the baking temperature of the lamp burners must be limited to prevent damage to the leads, and this limits the advantage of the baking process.
In another aspect, it is an object of the present invention to provide a novel method and apparatus for manufacturing lamps which avoids the baking temperature limitation imposed by the inclusion of non-substrate components in the device coated. In other aspects, it is an object of the present invention to provide to provide a novel method of baking coated lamp burner envelopes.
With respect to the losses associated with the defective coating of completed products, there will be “bad coating losses” in any coating process in which the coating is of unacceptable quality. Yet another disadvantage of performing additional manufacturing steps before the substrate is coated results in the loss of the entire lamp burner, including the components used as well as the time and expense incurred in performing the additional manufacturing steps. In lamp burners, for example, the electrical leads and the time positioning the leads and sealing the lamp burner envelopes represents a significant expense. Where the quality of the coating can be tested before any additional manufacturing steps are performed, the loss from a defective coating is limited to the substrate. In another aspect, it is an object of the present invention to provide a novel method and apparatus for manufacturing coated substrates in which the cost of bad coating losses is significantly reduced.
In the manufacture of certain products such as halogen lamps having a filament, it is known that an IRR coating on at least a portion of the surface of the halogen lamp burner improve the operating efficiency of the lamp, i.e., the IRR coating reflects the infrared radiation emitted in the light emitting chamber back toward the filament to raise the temperature of the filament and thereby reduce the power necessary to operate the lamp. The position of the filament relative to the lamp burner envelope is critical in optimizing the advantage in operating efficiency of the lamp from the use of an IRR coating on the lamp burner. Where the burner is assembled prior to coating, the existence of the IRR coating is not available in determining the optimum position of the filament. Known methods require the use of time consuming and complex apparatus to optically and mechanically position the filament prior to hermetically sealing the burner envelope to the leads. In yet another aspect, it is an object of the present invention to provide a novel method and apparatus for determining the optimum position of the filament of a halogen lamp relative to the lamp burner envelope. In other aspects, the methods and apparatus of the present invention are low in cost and easy to perform, facilitated by measuring the electrical resistance of the filament, and facilitated by measuring the power applied to the filament to maintain a constant temperature of the filament.
Where many of the disadvantages of completing the device prior to its coating are obviated by coating of the substrate prior to the further manufacturing steps, it becomes important to protect the coating from damage during the further manufacturing steps.
Where the substrate is coated prior to the additional manufacturing steps, there is the possibility of damage to the coating in the further manufacturing steps. For example in the manufacture of lamps where the lamp burner envelope is formed from glass or quartz, the step of hermetically sealing the burner envelope to the electrical leads includes the pinching of portions of the lamp burner envelope which have been raised to about 1700° C.–2000° C. Where the lamp burner envelope is formed from ceramic material, the step of hermetically sealing the burner envelope to the electrical leads includes the melting of a frit by raising its temperature to about 1700° C. Such temperatures may damage the coating. In another aspect, it is an object of the present invention to provide a method and apparatus for preventing damage to the coating formed on a lamp burner envelope during the sealing of the envelope. In additional aspects, this object may be realized by mechanical shielding and by a novel protective coating to both prevent damage to the IRR coating during the sealing of the lamp burner envelope and reduce the loss of infrared radiation during the operation of the lamp.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.